The M1911 cal. .45 ACP (Automatic Colt Pistol), invented by John M. Browning, was adopted in 1911 as the standard U.S. Service pistol. Since its development there have been no modifications to the standard issue service pistol that increases its accuracy capability. The standard issue service pistol has an accuracy capability of shooting a group of shots in a ten-inch circle at fifty yards. For accurate shooting this leaves much to be desired. Part of this inaccuracy is caused by the barrel within the barrel bushing not being in the same position after each shot. The barrel is therefore in a different position relative to the sights on the slide after each shot. This is caused by the loose tolerance between the barrel and barrel bushing. This loose tolerance characteristic has not been changed in standard production for fear of causing functioning problems which would yield an unreliable weapon in combat.
To improve this condition many methods have been tried with varying degrees of success. An early method was to punch or indent the barrel bushing around its circumference in an effort to tighten the bushing to the barrel. This is successful for a short period of time until the indentations wore off.
Another early method was to braze a bearing metal to the inside of the bushing to reduce the tolerance. It was effective but didn't hold up for very long.
The barrel bushings were manufactured with an undersize internal diameter which could be fitted to the specific barrel. This method works well in reducing the tolerance, but the cost of the bushing and machine work is too expensive.
As each method was tried, new developments came about. It was found that by reducing the barrel diameter 1/2" from the end of the muzzle 0.004"-0.005" (four to five thousandths), then fitting a special bushing with the undersize internal diameter, a greater degree of position lock up could be achieved which improved accuracy considerably. This method is still in use and works well to improve accuracy. It requires a considerable amount of machine work in turning down the diameter of the barrel, boring out the bushing and inserting another bushing which has the inside diameter matching the outside diameter of the barrel. This insert is silver soldered inside the bored out barrel bushing. This is a satisfactory method of reducing the tolerance between the barrel and the barrel bushing to afford a positive resting position of the barrel every time the weapon is fired. However, this substantial modification is time consuming, costly and requires skillful workmanship.
A recent development which aids accuracy to a minor degree is accomplished by manufacturing a barrel bushing which has spring steel properties. The bushing is split into four sections appearing like fingers which press in on the barrel. This reduces the barrel end play and adds to the accuracy capability. A problem arises as the barrel heats. Heat is transferred to the barrel bushing which changes the spring characteristics of the finger projections. This allows excessive movement of the barrel which defeats the purpose of the special barrel bushing.
When match barrels are manufactured, they are made oversize so they may be hand fitted to the specific barrel bushing and slide. The increased barrel diameter is manufactured into the barrel end, whereas before it was achieved through relieving the diameter 0.004"-0.005" (four to five thousandths) and decreasing the internal diameter of the bushing as previously described.